feat(battle-node): add NoOpBotParticipant

Silent participant for the Phase 3 Bot type. PushAsync swallows;
FrameEmitted never fires; RunAsync completes immediately. ViewerId is
the existing FakeOpponentViewerId const for consistency with scripted
lifecycle builders. Three tests lock the no-op contract.

SVSim.UnitTests/BattleNode/Sessions/Participants/NoOpBotParticipantTests.cs

@@ -0,0 +1,44 @@
+using NUnit.Framework;
+using SVSim.BattleNode.Bridge;
+using SVSim.BattleNode.Protocol;
+using SVSim.BattleNode.Protocol.Bodies;
+using SVSim.BattleNode.Sessions;
+using SVSim.BattleNode.Sessions.Participants;
+
+namespace SVSim.UnitTests.BattleNode.Sessions.Participants;
+
+[TestFixture]
+public class NoOpBotParticipantTests
+{
+    [Test]
+    public void PushAsync_swallows_without_firing_FrameEmitted()
+    {
+        var p = new NoOpBotParticipant();
+        var fired = 0;
+        p.FrameEmitted += (_, _) => { fired++; return Task.CompletedTask; };
+
+        var env = new MsgEnvelope(
+            NetworkBattleUri.TurnEnd, ViewerId: 1, Uuid: "u", Bid: null, Try: 0,
+            Cat: EmitCategory.Battle, PubSeq: null, PlaySeq: null,
+            Body: new ResultCodeOnlyBody());
+
+        Assert.DoesNotThrowAsync(() => p.PushAsync(env, noStock: false, CancellationToken.None));
+        Assert.That(fired, Is.EqualTo(0));
+    }
+
+    [Test]
+    public async Task RunAsync_returns_immediately()
+    {
+        var p = new NoOpBotParticipant();
+        await p.RunAsync(CancellationToken.None);
+        // If we got here, it returned.
+        Assert.Pass();
+    }
+
+    [Test]
+    public void ViewerId_is_FakeOpponent()
+    {
+        var p = new NoOpBotParticipant();
+        Assert.That(p.ViewerId, Is.EqualTo(SVSim.BattleNode.Lifecycle.ScriptedLifecycle.FakeOpponentViewerId));
+    }
+}